This invention relates to oscillating surgical saw and instrumentation systems, and more particularly to such systems used to shape bone, such as bone in a joint to conform it to a component of an artificial joint prosthesis.
This invention will be described in the context of artificial knees although it should be understood that the invention is not so limited. An artificial knee includes as one of its components a femoral component which replaces the condyles of the femur. An example of such a femoral component is illustrated in U.S. Pat. No. 4,892,547 to Brown for a Partially Stabilized Knee Prosthesis. As shown in FIGS. 1 and 2 of the '547 patent, reproduced here as FIGS. 1 and 2, the interior contours of a femoral component 10 has a plurality of surfaces which must match the surfaces of the femur after the femur has been prepared to receive femoral component 10. More specifically, femoral component 10 comprises a spaced-apart pair of downwardly convex bearing portions 12 which extend from the anterior side to the posterior side of component 10. The shapes of the outer surfaces of bearing portions 12 closely approximate the shapes of anatomical femoral condyles on the knee joint end of the femur. Femoral component 10 further comprises a generally vertically oriented patellar guide portion 14 which serves as a guide for the movements of a natural or prosthetic patella. The interior contours of femoral component 10 (which closely match the exterior contour of the end of the femur after the femur has been prepared to receive femoral component 10, i.e, the distal cut) are defined by generally vertical surface 16 on the posterior side of patellar guide portion 14, by posterior downwardly angled surfaces 18, 22 and 20 of bearing portions 12 and anterior intercondylar portion 21, respectively, by generally horizontal surfaces 24 and 26 of bearing portions 12, by posteriorly upwardly angled surfaces 28, 32 and 30 of bearing portions 12 and posterior intercondylar portion 31, respectively, and by vertically extending surfaces 34, 38 and 36 of bearing portions 12 and posterior intercondylar portion 31, respectively.
When femoral component 10 is implanted, the femur must be resected to fit the contours defined by internal surfaces 16-38 of femoral component 10. This is typically done by using an oscillating surgical saw and instrumentation system. The instrumentation guides the oscillating surgical saw as it is used to make the various resections in the femur so that the end of the resected femur matches closely the interior contours of femoral component 10. A technique and oscillating surgical saw and instrumentation system heretofore used in the knee replacement operation in which femoral component 10 is implanted is described in the brochure titled "AGC Total Knee System--Intramedullary with Distractor Surgical Technique" published by Biomet, Inc., ("AGC Total Knee System Brochure") which is attached hereto as Appendix A and incorporated herein by reference.
The oscillating surgical saw used to resect the femur usually has a blade which oscillates through a small arc on the order of four to six degrees at speeds of 15,000 to 20,000 cycles per minute. The excursion of the blade is necessarily short to permit the saw to cut in confined places. Moreover, the sharp teeth of the saw blade will cut rigid bone but if they contact soft tissue, the tissue will vibrate with the blade reducing the cutting of soft tissue.
Existing oscillating surgical saw and instrumentation systems used to resect the femur typically use cutting guides which have surfaces which transect the femur along planes which will match the planes in which the surfaces of the interior contours of femoral component 10 lie. In many cases, these surfaces are along slots which extend through the cutting block. However, the cutting block is typically held in place by hand and the saw guided along the cutting block by hand.
The problem with existing oscillating surgical saw and instrumentation systems is that vibration is transmitted from the blade of the oscillating surgical saw to the hands of the surgeon using the saw making it difficult to keep the saw aligned. More specifically, as the oscillating blade of the saw cuts into the bone, it will do so smoothly to a depth of about one centimeter. As the blade reaches a depth of about one centimeter, the blade begins to become trapped in the cut. When this happens, either the saw or the cutting block begins to oscillate. Consequently, the saw must be backed out of the cut to stop the vibration. To cut through the bone, the saw must be continuously inserted into and backed out of the cut. Otherwise, the blade will bind as described preventing the bone from being cut.
It is an objective of this invention to provide an oscillating surgical saw and instrumentation system that alleviates the vibration problem encountered by prior art systems.
It is also an objective of this invention to provide an oscillating surgical saw and instrumentation system where the saw, the instrumentation that guides the saw, and the bone are secured together against movement relative to one another in all planes except the plane in which the cut is being made.
It is also an objective of this invention to provide an oscillating surgical saw and instrumentation system where the instrumentation that guides the saw is affixed to the bone and the instrumentation, bone, and the saw are secured together against movement relative to one another in all planes except the plane in which the cut is being made and the instrumentation is configured to permit cuts through the bone in multiple planes without removal of the instrumentation from the bone.
An oscillating surgical saw and instrumentation system according to this invention has an oscillating surgical saw and instrumentation for guiding the saw. The oscillating saw has a body or handle having guide pin holders disposed on opposite sides thereof and extending longitudinally therealong. Retractable guide pins are mounted in the guide pin holders. Resilient means are disposed in each guide pin holder which force the respective guide pin mounted therein longitudinally outward. The system further includes instrumentation for guiding the saw. The instrumentation comprises at least one cutting block. The cutting block is affixed to the bone being cut and has holes for receiving the guide pins and can have slots through which the saw blade passes. The guide pin holes are preferably slots and lie in planes which are parallel to planes in which resected surfaces of the bone lie after they have been formed by cuts made to the bone.
When the saw is used to cut bone, the cutting block is secured to the bone and the guide pins inserted into the holes in the cutting block. The cutting block and guide pins cooperate to secure the saw against movement in all planes except the plane in which the saw is cutting to reduce the transmission of vibration from the bone being cut through the saw. The guide pin holes guide the saw blade as it cuts bone. As the saw blade cuts progressively deeper into the bone, the guide pins are forced into their guide pin holders so as not to interfere with the advancement of the saw blade into the bone.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.